Displays

While the behaviour of slow-moving landslides – response to seasonal precipitation, seismic shaking, etc. – is well described in natural mountainous environments, little is known on the influence of urbanisation on their dynamics. Yet, gradual urbanisation of hillslopes is commonplace in the outskirts of many cities of the tropics. Typically anarchic, construction on previously undisturbed slopes often initiates or enhances landslide activity, rapidly increasing the number of people exposed to landslide hazard. Aiming at studying how landslides respond to their progressive urbanisation, we here present a detailed analysis of the dynamics of a large, thousand-year-old slow-moving landslide located in the rapidly expanding city of Bukavu (eastern DR Congo). This slope failure developed in highly weathered lava layers hosts today more than 80 000 inhabitants; for many affected by incessant destruction of infrastructures and housing.

We used 4 years of temporally dense 3D kinematic data from satellite interferometry (MSBAS 3D), pixel tracking on satellite and Unmanned Aerial System (UAS) orthomosaics and aerial photograph analysis to examine the relationships between urbanisation, landslide activity and rainfall and seismic patterns. We found a closely tied relationship between subsurface pore-water pressure changes and surface velocities. Seasonal rainfalls are driving the kinematics of the landslide at the weekly timescale, despite the large (~30-100 m) depth of the landslide. Analysing landslide dynamics over the last 60 years, we observed an increased activity over a zone of the landslide that will rapidly become the fastest landslide unit. This destabilisation occurred in the ‘90s, alongside an intensification of the (informal) urbanisation of the hillslope, at a time when region’s violent conflicts and insecurity drove important rural-urban migration. Still the most active today, this landslide unit moves at paces of 0.5-3 meters per year, causing significant and persistent damages to infrastructures. We here argue that changes in water runoff, concentration and infiltration due to the anarchic and poorly maintained urban extension is modifying the long-term behaviour of the landside, rather than overloading due to buildings (often light and wooden structures) and infrastructures. The very quick response to pore pressure changes could also be associated to the dense urban fabric, even though the tropical characteristics of this environment (wet-dry seasons, high rainfall, very high weathering) should not be ignored. Our analysis help improve the evaluation of landslide hazard and mitigation in the area, but also across the other many cities of the tropics where similar environmental and societal conditions are met. These findings also have implications for our understanding of landslide dynamics and how humans are interfering with landscape evolution.

How to cite: Dille, A., Dewitte, O., Handwerger, A., Derauw, D., d'Oreye, N., Monsieurs, E., Samsonov, S., Smets, B., Kervyn, M., and Kervyn, F.: Urban growth changes the pulse of a large deep-seated landslide, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17805, https://doi.org/10.5194/egusphere-egu2020-17805, 2020.

Convex soil-covered hillslopes are ubiquitous in various tectonic and climatic settings and are often modeled based on a mass balance relating hillslope convexity to regolith transport and soil production. In order to account for chemical weathering of carbonate rocks and dust input to the regolith, two fluxes that are commonly neglected in settings with silicate-dominated bedrock,  we modify this mass balance.

We studied 7 study sites in carbonate rocks across an Eastern Mediterranean gradient in the mean annual rainfall (250 to 900 mm yr^-1) and dust flux (150 to 40 g m^-2 yr^-1). Combining cosmogenic ³⁶Cl-derived hilltops denudation rates with an estimate of the regolith chemical depletion and dust fraction based on immobile elements, we predict the hillslope curvature and compare our predictions with observations based on high-resolution airborne LiDAR.

Our results demonstrate that soft carbonates (chalk) experience faster denudation rates relative to resistant dolo-limestone. However, the harder carbonates are more prone to chemical weathering, which systematically constitutes around half of their total denudation.  Soil production rates exhibit a humped dependency on soil thickness, with an apparent maximum at a depth of 8-16 cm.

The observed hillslope curvature vary as function of rainfall and dust flux with a minimum at sub-humid sites with intermediate rainfall of  500-600 mm/yr. The predicted curvature based on our new mass balance is not far from the observed curvature, illustrating the prominent effects of dust flux and chemical weathering on hillslope morphology.  Our model also implies that drier sites in the south probably experienced a more complex history of regolith production due dust flux fluctuations.

By incorporating dust flux and chemical weathering to the classic hillslope evolution model we identify a complex relation between hillslope curvature, soil production, and climate. These two fluxes are not unique to carbonate bedrock and should be incorporated in hillslope evolution models.

How to cite: Ben-Asher, M., Haviv, I., Crouvi, O., Roering, J. J., and Matmon, A.: The convexity of carbonate hillslopes: the influence of climate, chemical weathering and dust flux , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11351, https://doi.org/10.5194/egusphere-egu2020-11351, 2020.

Soil erosion induced by heavy rainfall deeply affects landscape changes and human activities. It depends on rainfall distribution (e.g., intensity, duration, cumulative) and is controlled by the interaction among several factors including lithology, orography, hydrography, land-use, and vegetation. The Abruzzo piedmont-coastal area features a clayey hilly landscape that is historically affected by heavy rainfalls. In the last decades, it was affected by several heavy rainfall events in close sequence. In this work, we investigated some~1-day heavy rainfall (>35 mm/h and 100-220 mm/d) events occurred in 2007, 2011, and 2012 that affected the clayey hilly-coastal NE Abruzzo area. We analyzed cumulative rainfall, intensity and duration, mapping triggered geomorphological effects (soil erosion and accumulation) and evaluating average erosion.

The analysis provides contributions to the soil erosion assessment on clayey landscapes that characterizes the Adriatic hilly area, to the estimation of rainfall triggering thresholds for heavy soil erosion, and to a comparison of erosion in single events with rates known in the Mediterranean area. Comparing the different areas and cases investigated, the triggering threshold for heavy soil erosion shows an expected value ~100–110 mm. The estimated average soil erosion is from moderate to high (0.08–3.08 cm in ~1-day heavy rainfall events). The investigated relationships show a good correlation of sol erosion with cumulative rainfall, which results to be the most effective triggering factor, and a poor correlation with peak rainfall intensity. Finally, this work outlines the strong impact of soil erosion on the landscape changes in clayey hilly landscapes largely present in Mediterranean environments, such as in the Abruzzo and Adriatic hilly areas.

How to cite: Marsala, V., Piacentini, T., and Galli, A.: Analysis of heavy-rainfall-induced fast soil erosion: examples the NE Abruzzo clayey hills (Central Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15762, https://doi.org/10.5194/egusphere-egu2020-15762, 2020.

The accumulative fan was formed at the mouth of a well-developed system of erosive cuts in the lower Serteyka River valley in western Russia. The length of the fan reaches 70 m, and its thickness is up to 2 m. The erosive cuts (gullies) were formed on the steep and short slopes of the tunnel valley (transformed later into the river valley) and dissect the surface of the glaciofluvial plain for a length of ca. 110 meters. The absolute chronology of the development of that relief form was determined based on ¹⁴C and ²¹⁰Pb data set. It was started at the earliest in the second half of the 17^th century, and finished before the mid-19^th c. AD. These processes can be correlated therefore with palaeoenvironmental changes during the pessary of the Little Ice Age (LIA), as well as with human impact during the agrarian and industrial revolution in Eastern Europe. Studied accumulative fan is formed of deluvium with the insertion of the proluvium and an agricultural diamikton which is developed in ceiling part. The research based on the results of analysis of depth diversity of textural features (mean grain-size diameter, sorting index, skewness and kurtosis), geochemical features (chemostratigraphy determined on the basis of X-ray fluorescence spectroscopy – XRF) of the fan’s sediments and palaeoecological features (palynology analysis, subfossil Chironomidae and Cladocera analysis, plant macrofossil analysis) of biogenic deposits from under the fan.

How to cite: Piech, W., Kittel, P., Ginter, A., Mazurkevich, A., Hrynowiecka, A., Stachowicz-Rybka, R., Cywa, K., Mroczkowska, A., Pavlovskaia, E., Kazakov, E., Teltevskaya, Y., Sikorski, J., Okupny, D., Błaszczyk, K., and Kotrys, B.: Palaeoenvironmental development of the accumulative fan in Western Russia from the Little Ice Age to the present time, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1097, https://doi.org/10.5194/egusphere-egu2020-1097, 2020.

There is an ongoing debate about the main drivers of the Holocene landscape dynamics in Central Europe, i.e. when and where these were dominantly controlled by climatic (e.g. rapid climate changes) or anthropogenic factors. Investigations of colluvial and fluvial deposits are ideal to contribute to this discussion, given that the formation of colluvial deposits in Central Europe is often controlled by human activity, whereas the formation of alluvial deposits might be more influenced by climatic fluctuations.

In the forefront of a road construction intercalated colluvial and fluvial sediments with thicknesses up to 4 m were outcropped and studied during archaeological excavations led by the Bavarian State Office for Monument Conservation near Dettenheim in central Bavaria (southern Germany) in 2015. This investigated site is located next to the Fossa Carolina (Karlsgraben), a canal that was built at the end of the 8^th century AD to bridge the watershed between Rhine and Danube but that was never finished. We investigated the sediments using sedimentological, archaeological and geochronological (OSL) methods. After a period with fluvial activity during the Early Holocene, the landscape was mostly stable between ca. 10 and 2.5 ka, allowing the formation of soils. Although human activities next to the investigated sites originate from the Hallstatt period, the first interruption of the stable period only occurred during the La Tène Period when fluvial and colluvial deposits were formed. Subsequently, intensive colluviation occurred during the Migration Period/Early Middle Ages, followed by intensive colluvial and fluvial deposition that started since the High Middle Ages and continues until today. Our investigations indicate that human disturbance obviously led to an intensive landscape degradation during the La Tène Period, and the landscape was subsequently much more sensitive towards human and climatic fluctuations than before.

How to cite: von Suchodoletz, H., Kopecky-Herrmanns, B., Berg, S., Schneider, B., Fülling, A., and Zielhofer, C.: The Holocene landscape sensitivity of the central Bavarian Jura foothills towards climatic and human influences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20014, https://doi.org/10.5194/egusphere-egu2020-20014, 2020.

The variability in fluvial yield of clastic sediment is a useful metric of the upstream basin's geomorphic response to natural and anthropogenic landscape disturbances. It reflects an integrated signal of sediment mobilization and connectivity, that is the efficiency with which the mobilized material is evacuated by the sediment routing system. Average clastic sediment yield has also been used as a measure of mechanical denudation rates, although material storage along the routing system necessitates caution in such inferences.

Insight into the geomorphic responses to disturbances, provided by sediment yield analysis, is crucial for the understanding and management of river ecosystems. In the context of ongoing environmental change, intermediate-term system responses (spanning decades-to-centuries) to shifting disturbance regimes are of particular interest. Because of non-stationary conditions and high variability in fluvial sediment transport, knowledge developed based on short-term records of instrumented measurements is not readily transferrable to such longer time-scales. As a result, there is a need for more research focused on multi-decadal sediment yield patterns. 

This research addresses such a research need, by estimating clastic sediment yield from a forested mountain basin in NE Washington (USA) during a period of 107 years. To this end, we use historical aerial imagery and track, at the decadal resolution, sedimentation associated with delta growth following the construction of a dam. We interpret these data in the context of available records of streamflow and timber harvest operations, which constitute primary natural and anthropogenic disturbances. 

Preliminary results suggest relatively low sediment yield from the study basin, almost an order of magnitude lower than those reported from the coastal Pacific Northwest. We interpret inter-decadal variation in sediment yield estimates as indicative of interactive effects of flow forcing and land cover disturbance magnitude. We also believe that, because of variations of connectivity within the routing system, the sensitivity of sediment yield to disturbance at this time-scale is modulated by the location within the basin relative to its outlet.

How to cite: Cienciala, P., Bernardo, M. M., Haas, A., and Nelson, A.: Inter-decadal variation in clastic sediment yield from a forested mountain basin in relation to natural and anthropogenic disturbances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22517, https://doi.org/10.5194/egusphere-egu2020-22517, 2020.

Measurements of chemical and physical rates of landscape change in the tropics are rare. To address this data gap, a joint US/Cuban science team has worked together for two years sampling across the island of Cuba. Here, we report long-term cosmogenic erosion rates inferred from river sand paired with rates of chemical denudation estimated from river water solute loads. Together, these data define source-to-sink mass transport in 45 drainage basins in western and central Cuba and allow us to speculate on the role of agriculture on nutrient and sediment fluxes.

Rates of erosion determined from in situ ¹⁰Be concentrations range from <2 to ~80 m/My, are more varied in central than western Cuba, and do not correlate with chemical denudation rates. Comparison of cosmogenic erosion rates and sediment loads measured during the peak of industrial agriculture (1970s) suggests a modest increase in sediment yield likely reflecting intensive cultivation. Chemical denudation rates (n = 45) range from 42 to 302 tons/(km² yr) in central Cuba and from 11 to 125 tons/(km² yr) in western Cuba.  Chemical denudation rates and total dissolved solids are several times higher in central Cuba than western Cuba. River water is dominated by Mg, Ca, Na, K, and Si in both areas.

Although cosmogenic erosion rates are often interpreted as total landscape denudation, we find in some Cuban drainage basins that ¹⁰Be-based erosion rates underestimate total landscape denudation. Considerable discordance (12-60X) between erosion rates and chemical denudation rates in five central Cuban basins suggests that significant mass loss by solution is not reflected by cosmogenic-based erosion rates. In 2 of these basins, erosion rates calculated from duplicate measurements of ¹⁰Be (1.4 & 2.5 m/My) and ²⁶Al (1.7 & 2.9 m/My) were ~50X lower than chemical denudation rates (89 & 108 m/My). Both ²⁶Al and ¹⁰Be concentrations indicate long term, near-surface (>>100 ky) quartz residence; stream water geochemical data are consistent with the presence of evaporite deposits. We suspect that rapid chemical denudation enriches basin sediment in quartz, which lingers at or near the surface in these low slope (0.5°) basins.

Despite centuries of agriculture, the impact on Cuban river biogeochemistry is limited. Although river water in many central Cuban rivers has high levels of E. coli bacteria, likely sourced from livestock, concentrations of nitrate are far lower than other areas where intensive agriculture is practiced, such as the Mississippi River Basin. This suggests the benefits of Cuba’s shift to conservation agriculture after 1990 and provides a model for more sustainable agriculture worldwide.

How to cite: Bierman, P., Campbell1, M. K., Schmidt, A., Sibello Hernández, R., García Moya, A., Cartas Aguila, H. A., Bolaños Alvarez, Y., Guillén, A., Dethier, D., Massey-Bierman, M., Corbett, L., Caffee, M., and Alonso-Hernández, C.: ¡Cuba! New Chemical and physical denudation rates define source-to-sink mass transport and anthropogenic impacts on nutrient loads for the largest Caribbean nation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12355, https://doi.org/10.5194/egusphere-egu2020-12355, 2020.

Knowledge of river basins sediment yield at a continental scale, and accumulation in sedimentary basins (sinks) provides useful information for quantitative models of landscape evolution, geochemical and sediment mass balance studies for estimating continental and regional net erosion intensities, to quantify the fluxes of sediments exported to the Ocean. It also provides a crucial understanding of a variety of environmental and engineering applications. Although several estimations exist on the sediment fluxes of large rivers,  the role of continental sedimentary basins and fluvial environments (large rivers and megafans) acting as major sedimentary sinks is still partially understood. The assessment is additionally complicated by the human activities that contribute to modifying the original rates of production, trapping, and transference of sediments at continental scales.

South America is an ideal place to discuss these aspects because it contains a) the longest mountain chain on the planet, the Andes; b) the longest and more extensive foreland systems, c) huge lowlands/plains, d) the largest rivers, e) the largest megafans, f) major intracratonic, sedimentary basins. Simultaneously, the rivers basins are being submitted to extreme environmental pressure by the construction of dams, land use/land cover changes (LULC),  mining, etc.

Here, quantitative results on continental sources and fluxes are presented, with a focus on the role of the biggest source areas and the largest trapping systems at a continental scale such as megarivers and megafans.  Particular attention is devoted to sediment budgets of large rivers that have been intensively modified by human activities in recent times (dams, deforestation, etc) or that are vulnerable to the potential construction of dams.  

How to cite: Latrubesse, E.: Continental sediment sources, sinks, and the human factor in large tropical rivers: the case of South America, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4401, https://doi.org/10.5194/egusphere-egu2020-4401, 2020.

The Amazon River is an important source of the sediment that is transported and accumulated along the coast of Suriname. As such it is an important factor in maintaining the coastline as this sediment is deposited in mud banks that move towards the shore and coalesce with it, thus preventing coastal erosion. Accordingly, a steady and adequate supply of sediment from the Amazon river is required especially considering increased coastal erosion rates that may occur as a result of rising sea levels due to climate change. Yet at the same time, climate change may alter the hydrological regime of the Amazon and influence its transport capacity, affecting sediment transport to the mouth and coast. Furthermore, the sediment supply to the river may be altered as a result of land cover changes and other anthropogenic activities, including deforestation and sediment trapping in existing and future planned reservoirs.
Studying the transport of sediment from source to sink and quantifying how future changes affect the mean rate of sediment supply to the Surinam coast and its variability will lead to a better understanding of the intricacies involved. We use a spatial-temporal process-based model together with a set of plausible scenarios of future change based on combinations of the Shared Socioeconomic Pathways (SSP) and the Representative Concentration Pathways (RCP). In this study, we used two models: PCRGLOB-Set and PCRGLOB-WB. PCRGLOB-SET is based on the RUSLE equation and is used to assess the local sediment supply including the effects of land cover changes. PCRGLOB-WB simulates hydrological responses and changes under climate and land-use change. Moreover, PCRGLOB-WB is used to determine the trapping efficiency of reservoirs. The PCRGLOB-WB model was applied to a business-as-usual scenario for the 21st century (SSP 2 with RCP 6.0) and we considered uncertainty in the projected climate by using 5 Global Climate Models (GCMs). We apply the model to different future scenarios considering climate, socioeconomic and land-use change. For validation, the observations of six stations along the Amazon river were compared to the estimations of the models for the historical period (1971-2010), which also serves as a reference run to evaluate changes in sediment production and sediment yield. 

How to cite: Naffaa, S., van Beek, L. P. H. (., E.Dunn, F., and de Jong, S.: Modeling the changing sediment yield of the Amazon under climate change and deforestation scenarios and the possible impacts on the Guiana coast, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18621, https://doi.org/10.5194/egusphere-egu2020-18621, 2020.

Western Norwegian fjord-valley systems represent archives of changes in sedimentary processes, and typically exhibit a pronounced change in depositional environment related to the transition from glacial to interglacial conditions. During a glacial situation, the fjord-valley system is emptied of its sediments, indicating that most sediments present in the fjord today, was deposited during and after the retreat of the last deglaciation. The purpose of our investigations is to gain a better understanding of the volumes and frequencies of mass transport deposits (subaquatic mass movements such as mass flows, debris flows, slides, slumps, and turbidites) in a recently glaciated fjord-valley system since the deglaciation (approx. 11 700 years BP) by looking at Fjærlandsfjorden, a tributary fjord of Sognefjorden in western Norway. The fjord-valley system consists of steep hillslopes and deep fjord basins with reliefs of up to 1600 meters. Jostedalsbreen, the largest glacier on mainland Europe (ca. 473 km²), currently feeds into the catchment of the fjord basin.

Here we present results from a cruise with R/V G.O. Sars in 2018, where sediment cores, TOPAS seismic profiles and bathymetric data were collected from Fjærlandsfjorden. The integration of high-resolution seismic (<30 cm vertical resolution) and bathymetry (3-5 m resolution) allows us to estimate the total volume of sediments within a fjord setting. By revealing when and how the sediments are deposited, we can establish sedimentation rates with a high spatial and temporal resolution within the fjord basin. X-ray Computed Tomography (CT-scanning) has been particularly useful to characterize sedimentary deposits as it allows for 3D visualization and analysis with ultra-high-resolution (50 μm voxel size) allowing us to see individual silt-sized grains in the sediment cores.

Seismic data reveal that the Fjærlandsfjorden basin infill consists of basal till, overlain by a thick, acoustically well-laminated glacimarine unit (up to a maximum thickness of ~105 meters thickness), occasionally disrupted by acoustically transparent lenses interpreted to be mass transport deposits (rock avalanches and debris flows). A 2-3 m thick hemipelagic unit drapes the glacimarine unit. Results reveal that ~90 % of the total sediment volume within the fjord basins was deposited as meltwater plumes during the retreat (mainly calving along the fjord) of the margin of the last glacial ice sheet. The retreat began at the mouth of Sognefjorden at the termination of the Younger Dryas Chronozone around 11 700 cal. yrs BP, to a frontal position at the head of Fjærlandsfjorden around 10 700 cal. yrs BP. The remaining volume of sediments are divided into mass transport deposits (MTDs) such as avalanches, debris flows, and flood-related turbidites as well as hemipelagic sedimentation. The largest MTD is a massive rock avalanche measuring up to 5 million m³ that most likely caused a large tsunami when it occurred.

How to cite: Thuesen, T., Haflidason, H., Helland-Hansen, W., Nesje, A., Klette, A. K., and Eide, C. H.: Sediment budget in a recently glaciated western Norwegian fjord, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21537, https://doi.org/10.5194/egusphere-egu2020-21537, 2020.

The Ayeyarwady River in Myanmar is one of the last free flowing large rivers in the Southeast Asian region. It hosts some of key biodiversity hotspots in the Indo-Burma conservation corridor. River impoundments are restricted mainly in the small tributaries, allowing natural flow regime in the main channel. It also serves as one of main transportation River morphological change and extreme floods events are common occurrence in the basin owing to seasonal dynamics imparted by monsoonal rainfall in river flow and sediment patterns

Such yearly morphologically change pose threat to thousands of villages located along the banks of the Ayeyarwady River in addition to the risk faced by agricultural land and navigation routes. In addition, the interconnections between hydrology, morphological change and flood patterns of Ayeyarwady River has be rarely studied with the aim of supporting decision making and influencing policy change. This critical knowledge gap can aid in providing vital information towards integrated management of the Ayeyarwady River system for multiple uses and users.

Using a suite of remote sensing-based monitoring tools and hydrological models we assess the interconnections between the biophysical features of the Ayeyarwady River Basin driving the river morphological change. Using long term remote sensing data (Landsat), we assess morphological change at various time scales (seasonal, yearly, decadal and long term) to identify reach hotspots within the river to categorize the risk from erosion. Erosion and deposition rates as well as channel migration rates were estimated for the entire river length seasonally. The erosion estimates are consistently larger than the deposition rates in recent years, which are in line with the observed widening of channel at different reaches. We aggregated Landsat and MODIS based flood maps to create a long-term time series covering entire Ayeyarwady Basin. A lumped hydrologic model was used to assess the historical (1989 to 2019) flow dynamics within the river system.

One key conclusion is that, there exists a strong relation between the reaches prone to large morphological change and high to medium flood risk areas within the basin. In Ayeyarwady, the management of river morphological change and flood management are undertaken separately. The outcome of this study provides a key knowledge base emphasizing that river morphological change and flood patterns are strongly correlated and need to managed as an interrelated problems. The flow patterns and sediment budgets of the Ayeyarwady River are undergoing change from the intensifying anthropogenic activities such as upstream landuse change, which are likely to affect the river morphological hotspots. We further assessed the potential for using “room for river” concept to manage morphological hotspots by estimate the economic implications of converting productive agricultural lands adjacent to the riverbanks into forested sections to drive the policy thinking towards adopting nature based solutions for better channel management.

How to cite: Matheswaran, K., Bhatpuria, D., and Piman, T.: Unravelling the river morphological – flood pattern linkages in Ayeyarwady River Basin, Myanmar, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21095, https://doi.org/10.5194/egusphere-egu2020-21095, 2020.

Water scarcity threatens people in various regions, and has predominantly been studied from a water quantity perspective. However, the provision of water for human uses and environmental health is dependent on both sufficient water availability but also appropriate water quality for the intended use.

Our study presents the first estimates of global water scarcity driven by both water quantity and water quality issues and including impacts of desalination and treated waste-water reuse. We have developed a new water scarcity framework combining model simulations of multiple global hydrological models and global surface water quality models (water temperature, salinity, organic pollution, nutrients) and spatially-explicit datasets of desalination and treated wastewater reuse capacities globally.

Our results show that 40% of the world’s population currently lives in regions with severe water scarcity, which is driven by a combination of water quantity and quality issues. Impacts of water quality are in particular high in river basins in eastern China. Here, excessive water withdrawals and polluted return flows degrade water quality, exacerbating water scarcity. Our results show that expanding desalination and treated wastewater reuse capacities can strongly reduce water scarcity in most river basins, although the side-effects (e.g. brine production, high energy demands and costs) must be considered. We conclude that effective water scarcity reduction requires that we expand our focus from conventional measures, which mainly focus on improving water supply for sectoral uses, to solutions that also promote water quality improvements.

How to cite: van Vliet, M. T. H., Jones, E. R., Flörke, M., Franssen, W. H. P., Hanasaki, N., Wada, Y., and Yearsley, J. R.: Global water scarcity reduction requires water quality solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2718, https://doi.org/10.5194/egusphere-egu2020-2718, 2020.

Suspended sediment yield values from glaciated mountain catchments are often among the highest in the world. Nonetheless, the sediment sinks, sources and dynamics can be highly variable in such environments under climate change. The aim of this study is to quantify the different suspended sediment sources of the Djankuat river catchment (A=9,1 km²). This small high mountain stream is located in the Caucasus mountains. It is partly glaciated with steep slopes, alpine meadows and glacial-nival terrains. Large scale geomorphological mapping of the catchment was undertaken using drone images and field surveys. This allowed to identify the main sediment sources as well as key pathways of the sediment to the river. In addition, about 50 composite surface (topsoil) and subsurface (riverbanks) samples were collected within the catchment area to characterize the different sediment sources. Two different mixing models (fingerPRO and SIFT) were applied to evaluate the relative contribution of these sources to river suspended sediment yield. Furthermore, direct measurements of water discharge and turbidity were undertaken at two gauging stations. One of them was located near the edge of glacier and the other about 1 km downstream. This allowed to evaluate the relative contribution of the glacial and proglacial part of the catchment to the total suspended sediment yield. Overall, these independent approaches resulted in relatively similar estimates of the relative importance of the different sources to suspended sediment yield. It has been established that the proportion of glacial material (generated by glacier erosion, including subsurface and supraglacial runoff) in total suspended sediment load decreases from 80-90% at the first 50-100 m from the glacier edge to 60-70% at a distance of 700-1000 m.

This study was funded by the Russian Science Foundation, project no. 19-17-00181

How to cite: Tsyplenkov, A., Kharchenko, S., Vanmaercke, M., and Golosov, V.: Application of geomorphological mapping and fingerprinting to identify the different suspended sediment sources of the glaciated Djankuat catchment, Caucasus mountains, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-385, https://doi.org/10.5194/egusphere-egu2020-385, 2020.

Climate warming in high altitude regions is causing rapid retreat of mountain glaciers that might likely accelerate in the near future. As much as 99 % of all tropical glaciers are in the Andes, of which approximately 70% concentrate in the Cordillera Blanca range (Perú) where Parón Lake is located at the foot of Artesonraju Glacier. In the last century the glacier surface area in the Cordillera Blanca has decreased by around one third. Melting glaciers is leading to the formation of new proglacial lakes that are increasing in number and volume playing a key role in regulating water storage and supply to glacier-fed rivers. Glacier recession results in changes in paraglacial environments where processes acting on new exposed surfaces of highly reactive rocks are highly dynamic. These processes can generate important amounts of sediments which can threaten water quality and biodiversity. Environmental concerns strengthen the need for assessing the provenance of fine sediment. To this end, in the frame of the IAEA INT5153 project a two week field survey of the Parón Lake area was carried out in October 2016 to recognize the main glacial landforms which had direct connectivity to the drainage system into the lake. The main glacial landforms, which included moraines, colluvium, glacio-fluvial terraces and alluvial fans that had developed after different stages of glacier retreat from the Last Glacial Maximum to the Little Ice Age, were mapped. For identifying the main provenance of sediments, a total of 40 composite soil and sediment samples (from 0-3cm depth) were collected as sources from representative sites on the main glacial landforms. In addition a total of 9 sediment mixtures including composite channel bed sediments and suspended sediments were collected. Channel bed mixtures were sampled along the river system between the tongue of Artesonraju Glacier and the end of Parón Lake while suspended sediment samples were also collected from the lake margin half way along its length. For applying fingerprinting methods we analysed 6 radioisotopes (2 FRNs and 4 ERNs) and a total of 28 stable elements. The preliminary unmixing results modeled with FingerPro after applying a novel procedure for tracer selection (Lizaga et al., 2020) identified different provenances in each of the sampled points depending on the proximity and connectivity of the glacial landforms. Moraines and alluvial terraces were main contributors in two of the channel mixtures while a relatively greater apportion from colluvium and alluvial fans was found in the lake sediment mixture located at the end of the Parón Lake. Unmixing results for the suspended sediments confirmed the higher contributions from glacio-fluvial terraces and colluvium in the middle part of the lake suggesting that the direct connectivity of glacial landforms was a key control of fine sediment supply to the lake. Further research is needed to assess changes of sediment sources during wet seasons or rainfall peaks in high water and flood regime to gain more comprehensive information on the temporal and climate variability of fine sediment supply.

How to cite: Navas, A., Lizaga, I., Gaspar, L., Stott, T., Mavlyudov, B., and Dercon, G.: Modeling the provenance of fine sediments in Parón Glacier Lake (Cordillera Blanca, Perú) by using a new procedure of tracer selection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3270, https://doi.org/10.5194/egusphere-egu2020-3270, 2020.

Climate change, human activities and other perturbations (like, e.g., fires, earthquakes) are influencing existing patterns of weathering, erosion, transport and deposition of material across defined landscape components and units. While it is still a challenge to develop an improved scientific understanding of how such changes interact and affect hillslope and fluvial processes, the connectivity between hillslope and fluvial systems and within landscapes, as well as contemporary denudation rates, source-to-sink fluxes and sedimentary budgets, this kind of quantitative analyses promise to be an efficient framework to assess the impact of environmental changes and disturbances to sediment dynamics and to evaluate landscape sensitivity. Our current knowledge on drivers and quantitative rates of contemporary sediment dynamics and denudation forms the basis for understanding and predicting the consequences of ongoing and accelerated environmental changes.

Ongoing GFL research activities on the current morphoclimate, on sediment sources, sediment storage, and on drivers, the spatiotemporal variability and rates of chemical and mechanical hillslope and fluvial denudation in three selected Mediterranean catchment systems in eastern Spain are presented. The Quisi, Pou Roig and Mascarat catchment systems in the Calpe region in eastern Spain are located in a mostly mountainous and/or anthropogenically affected environment. The three selected catchment system have a similar lithology (mostly limestone) but show significant differences with respect to catchment morphometry, sedimentary covers and the degree of anthropogenic modification. The activation of relevant sediment sources, sediment transfers, the intermittent runoff, and fluvial processes and transport are almost entirely controlled by pluvial events. During pluvial events of defined magnitudes, defined parts of the catchment areas and defined sediment sources are activated. Our year-round investigations include detailed geomorphological mapping combined with detailed statistical analyses of existing meteorological high-resolution data and the continuous observation and monitoring of atmospherical inputs, runoff events, and of sediment mobilisation and transfers on slopes and in stream channels using a combination of different automatic and manual observation, monitoring and sampling techniques. Our quantitative results on drivers and the spatiotemporal varianility of atmospheric solute and sediment inputs, of chemical and mechanical denudation, and on sediment storage and sedimentary budgets within the three different catchment systems contribute to an advanced understanding of key drivers and rates of contemporary sediment dynamics and denudation in this Mediterranean environment, and provide the basis for improved predictions of possible effects of climate change and anthropogenic impacts on contemporary denudation rates and hazardous earth surface processes in this morphoclimatic region.

How to cite: Beylich, A. A. and Laute, K.: Sediment sources, denudational processes and sedimentary budgets in three Mediterranean catchment systems in eastern Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3492, https://doi.org/10.5194/egusphere-egu2020-3492, 2020.

Erosion by emerging groundwater (i.e., seepage erosion or groundwater sapping) is the primary mechanism initiating stream channels (so-called seepage channels) and headward growth in lowland areas with a high infiltration capacity of sediment where the surface runoff is relatively rarely observed. Around groundwater outflows, as a result of the impact of denudational processes, develops an alcove, which is an amphitheatrical depression, often of steep slopes, separated from the slopes of the initial depression with clear edges. A spring-formed alcove is the upper boundary of a concentrated flow of water and sediment transport between well-marked channel margins. The influence of groundwater remains one of the least understood factors in the landform evolution in the postglacial zone of Western Pomerania (north-western Poland).

Morphometric and lithological surveying of about 80 spring-formed alcoves were studied in the southern part of the Parsęta catchment (NW Poland) made it possible to identify morphological effects of seepage erosion which are combined with surface wash and mass movement processes. The co-occurrence of various denudational processes in the headwater zones produces variations in the accumulation conditions, and as a result, a diversity of deposits. The mineral series includes erosional pavements, colluvium, and alluvial deposits. Changes in hydrodynamic conditions are favourable to organic accumulation (peats and organic-mineral muds) as well as  chemical and biochemical deposition (calcareous tufa and precipitation of Fe-oxides). Seepage channels grow when they attract enough groundwater to remove clastic material from the heads. Depending on the discharge volume of the outflow from the ten observed spring-formed alcoves (1-73 L/s), products of mechanical denudation (4-54 mg/L) are transported from the slope system to the fluvial system.

The morphometry of the spring-formed alcoves as well as deposits found in them reflect stages of their development. Changes in the development of the channel heads occur as a result of variations in the groundwater table that are due to changes in climatic conditions or land use. The determination of the place and formation of the beginning of a river channel initiated by groundwater outflows is of key importance for the modelling of the development of a stream network.

How to cite: Mazurek, M.: Spread of denudational processes in seepage channels in a postglacial area (north-western Poland), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5933, https://doi.org/10.5194/egusphere-egu2020-5933, 2020.

Since the end of the Little Ice Age (LIA) glacial advance, mountain glaciers of temperate zone have experienced an accelerated retreat accompanied by an increased production, transport and accumulation of glacial sediments. In these deglacierized areas, the development of a chronology for sediment deposition in the glacier forefronts remains challenging. Indeed, various dating methods are applicable but only few of these are capable to cover the last centuries with a high resolution. Amongst these methods, dendrochronological dating offers the possibility to reconstruct minimum ages of the moraines with a yearly resolution, providing a detailed chronology for glacier dynamics. Tree-ring dating relies on the assumption that the age of the oldest tree represents an estimate of the minimum age of the moraine resulting from the glacier movements. Although the Caucasus Range is one of the most heavily glaciated areas of temperate zone, field evidences and historical records point out that mountain glaciers are already in accelerated decline in response to climate warming since the LIA. In this respect, the main purpose of our study is to document historical changes of the Challaati glacier, located in Mestiachala river basin, over the last centuries by using tree-ring dating coupled with field survey investigations. The methodology involves the application of dendrochronology and geomorphological field mapping completed by GPS records. A total of 120 living Scots pine trees (Pinus sylvestris) growing on glacier forefield have been sampled with Pressler increment borers of various lengths. Tree-ring widths were measured with an accuracy of 0.01 mm using a LINTAB 5 measurement station (Rinntech, 2019). The quality of the visual cross-dating was statistically checked using the COFECHA program. In order to reduce uncertainties in dating the colonization age of moraines, various corrections were applied, including: (i) the reconstruction of the number of missing rings to the pith (pith offset estimation); (ii) the determination of age-height relationships for the study site (tree age estimation at the coring height corresponding with years a sapling needs to grow to breast height); and (iii) the determination of the ecesis, which is related to the period from the stabilization of the moraine surface to the germination and establishment of the first trees. Tree-ring analyses coupled with GPS records and geomorphological mapping of glacier forefield allowed us to reconstruct multiple stages of glacier recession, and also to calculate the retreat rates since the end of LIA. Therefore, this study highlights the usefulness of tree-ring dating coupled with field survey investigations to improve our knowledge and understanding of glacier forefield changes, but also to provide a robust dataset for the modelling the retreat of glaciers at various scales.

This work represents a contribution to the joint research project ‘‘Impact du changement climatique sur les glaciers et les risques associés dans le Caucase géorgien (IMPCLIM)’’ co-funded by the Agence Universitaire de la Francophonie (AUF) and Institutul de Fizică Atomică (IFA), Romania.

How to cite: Pop, O. T., Răchită, I. G., Germain, D., Rikadze, Z., Holobâcă, I. H., Khuntselia, T., Alexe, M., Elizbarashvili, M., Gaprindashvili, G., Ivan, K., and Tielidze, L.: Tree-ring dating of colonized moraine surfaces in deglacierized areas of Greater Caucasus Mountains , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6711, https://doi.org/10.5194/egusphere-egu2020-6711, 2020.

Rivers have been a crucial part of human existence and the cradle of ancient civilizations. Historically, all cities developed along river banks. Rivers have played a seminal role in structuring cities the world over. India is recognized as a river nation and has had a long history of mystical affiliation with its rivers. Here rivers are considered sacred and venerated. All human activities and rituals are innately associated with the riverfront. Riverfronts have functioned as crucial socio-cultural religious spaces. In today’s times however Rivers present a gory picture of neglect. Fresh water is polluted by domestic, industrial, agricultural and religious waste. Fortunately, people  over the world have begun to realize the importance of rivers and concentrated efforts to ecologically rehabilitate and restore them are underway. In India, such efforts are mostly hinged on channelizing the riverbank and providing a space for recreation for city dwellers. Activists and water proponents, however, contest this approach and term it to be a mere initiative focussed towards river beautification rather than river rehabilitation. Such initiatives are not necessarily ecologically responsive and sustainable. India has been one of the leading participants of the United Nations and is dedicated to the UN's 2015 sustainable development goals (SDGs). Under SDG 6 and SDG 11, India strives to boost its water bodies, water quality and provide a comprehensive sustainable solution. India initiated the Smart City Projects (SCP's) in 2015, focussing on cities ' overall sustainable development'. Under this project, a total of 100 cities have been identified and more than 60 cities have a plan for riverfront development. These initiatives are targeted at reducing water pollution, providing aid to the riverbank and improving the connect between the city and its river. This paper aims at reviewing the recent Riverfront development proposals in India under the smart city mission and develop a set of indicators as a framework that allows future communities to reclaim their river and river edges in a sustainable manner. Research is conducted in two stages. Phase one is to establish a framework based on the principles of urban design and urban planning policies in India and assess the planned riverfront project. Phase two suggests a multi-criterion sustainability framework in the context of Indian rivers and validate its application using the community discussion process. Discussions involve Indian government officials’ scholars from a variety of disciplines, engineers, designers, and the general public. This framework aims to direct developers, architects, PWDs, environmental authorities, towards sustainable restoration/rehabilitation strategies in the context of Indian rivers. 

Keywords: Riverfront development, River Rehabilitation, River Restoration, Sustainability, Channelization, Smart City Projects

How to cite: Bais, R. and Suneja, M.: Guiding Sustainable Development along Rivers in India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8155, https://doi.org/10.5194/egusphere-egu2020-8155, 2020.

Irrespective of administrative boundaries, river basins are natural spatial units covering the entire land area. They provide many resources, including freshwater, which is essential for the environment and human society, as well as irrigation water and hydropower. At the same time, river basins are highly pressured i.e. by human induced environmental changes, such as deforestation, urban expansion, dam construction, as well as climate change induced sea level rise at estuarine regions and extreme events such as droughts and flooding. Therefore, monitoring of river basins is of high importance to understand their current and future state, in particular for researchers, stake holders and decision makers. However, land surface and surface water variables of many large river basins remain mostly unmonitored at basin scale. Currently, only a few inventories characterizing large scale river basins exist. Here, spatially and temporally consistent databases describing the evolution and status of large river basins are lacking. In this context, Earth observation (EO) is a potential source of spatial information providing large scale data at global scale. In this study, we provide a comprehensive overview of research articles focusing on EO-based characterization of large river basins and corresponding land surface and surface water parameters, we summarize the spatial distribution and spatial scale of investigated study areas, we analyze used sensor types and their temporal resolution, and we identify how EO can further contribute to characterization of large river basins. The results reveal that most of the reviewed research articles focus on mapping of vegetation, surface water, as well as land cover and land use properties. In addition, we found that research articles related to EO applications hardly investigate study areas at the spatial scale of large river basins. Overall, the findings of our review contribute to a better understanding of the potentials and limitations of EO-based analyses of large river basins.

How to cite: Uereyen, S., Bachofer, F., Huth, J., Klein, I., and Kuenzer, C.: Remote Sensing of Large River Basins, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9084, https://doi.org/10.5194/egusphere-egu2020-9084, 2020.

Anthropogenic disturbance is one of the main drivers of contemporary river adjustment. In mountain streams, information and prior work on post-disturbance recovery rates is limited, compared to lowland counterparts. The BEDFLOW initiative aims to investigate fluvial morphodynamics along the mountain portion of the Sillaro River (138 km²), Northern Apennines, to guide local strategies of sediment management at the basin scale and improve environmental quality of this fluvial system. Of particular interest is the understanding of the historical and contemporary response of the Sillaro River to gravel mining activities, which focused in the mid-to-lower portions of the river between the mid-1940s and the early 1980s. To this end, BEDFLOW adopts a multi-scale approach that integrates: (1) historical analysis of planform channel changes across the entire montane channel main stem over the past 100 years; (2) hydraulic and bed texture characterization of 14 representative reaches that encompass drainage areas comprised between 2.7 and 113 km²; and (3) flood-event scale, RFID bedload monitoring in two reaches, complemented by topo-photogrammetric surveys of the subaerial and submerged channel bed.

Analysis of historical channel changes was conducted by mapping active channel width on historical topographic maps (1928) and across 11 sequential aerial photo sets (1954, 1969, 1976, 1988, 1996, 2000, 2008, 2011, 2014, 2016 and 2018), along a valley segment of about 26 kilometers (i.e., 35 homogeneous reaches). Vertical channel adjustment was assessed by comparison of long profiles extracted from 1928 and 1976 topographic maps.

Preliminary results indicate that the river has experienced intense channel narrowing between 1969 and 1996. This pattern has progressively slowed down, even though narrowing continues until today. Cumulatively, reduction in active channel width has been highest in the distal most unconfined reaches, where median width has decreased from >120 m in 1954 to about 20 m in 2018, intermediate in semi-confined reaches (from 99 m to 28 m), and least in the upper confined reaches (from 30 m to 15 m). In the semi-confined and unconfined reaches, where most of the gravel mining took place, channel pattern has changed from braided to wandering and/or from wandering to single-thread. Today, after about 35 years since in-channel gravel mining became interdicted, the river still exhibits signs of incomplete recovery, as bedrock sporadically outcrops amidst mid channel bars, formerly occupied by braided plains.

The two monitoring reaches, which are active since February 2020, have contrasting morphology and degree of hillslope coupling. The upper one (drainage area = 35 km²) is a riffle-pool, uncoupled reach, characterized by a fine-to-coarse gravel texture and a channel slope of 0.8 %. The lower one (50 km²) is a transitional reach with dominantly plane-bed morphology and lesser riffle-pool and step-pool stretches; it is characterized by fine gravel to boulder texture, and by a channel slope of 1.5 %. The b-axis of deployed tracer stones spans from 36 to 180 mm.

The Sillaro River basin functions also as a training site for students. This work, as part of the projects BEDFLOW and BEFLOW PLUS, is partially funded by Fondazione Cassa di Risparmio in Bologna.

https://site.unibo.it/bedflow/en

https://site.unibo.it/bedflow/it

How to cite: Brardinoni, F., Bernardi, A. R., Bonazzi, F., Caputo, G., Hassan, M., Pittau, S., and Reid, D.: BEDFLOW: integrating river morphodynamics in the Sillaro River across spatial and temporal scales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10800, https://doi.org/10.5194/egusphere-egu2020-10800, 2020.

The lower Mississippi continues to adjust to upstream human impacts and channel engineering. Fluvial islands (vegetated sandy bars > 1 ha) are a key mode of riverine adjustment along the Lower Mississippi, and have substantially increased in number and size over the past five decades, from 112 in 1965 to 295 by 2015, which can largely be attributed to groyne construction. This study examines the morphologic evolution of fluvial islands from Cairo, IL to the downstream-most island at about Bonnet Carre Spillway (~5 km upstream of New Orleans). The analysis utilizes lidar DEMs, historic air photos, and adjacent hydrologic (stage) data. Additionally, changes to island vegetation were examined by comparison of the Normalized Difference Vegetation Index (NDVI) calculated from analysis of Landsat imagery for 1996 with 2014.

While each island is somewhat unique and influenced by local scale factors, there are clear geomorphic differences between new islands and older islands. New islands (did not exist in 1965) do not have appreciable natural levees and the island high point is at about flood stage. Older islands that are stable and larger have formed natural levees, which are higher than average flood stage and often higher than the adjacent floodplain surface. The downstream slope of new islands is an order of magnitude higher than old islands, averaging 0.0028 m/m and 0.0009 m/m, respectively. This is likely attributed to the downstream growth of islands, increasing in length and aggradation on the downstream flank. Additionally, between 1996 and 2014 island vegetation matured, with the area of moderate vegetation decreasing at the expense of an increase in denser vegetation. A comparison of the NDVI for the same islands in 1996 and 2014 between Vicksburg and Red River Landing reveals an increase in vegetation health and density. While the area of islands classified as sandy (NDVI 0.1-0.2) and scrubby (NDVI 0.2-0.3) vegetation did not substantially change between 1996 and 2014, the amount of dense vegetation (NDVI > 0.5) considerably increased (from 3.2 km² to 9.8 km²) as the amount of moderate vegetation (NDVI 0.3-0.5) decreased (15.1 km² to 8.4 km²). The increase in vegetation density can be attributed to the increased amount of time since island formation was initiated, and a maturation of the island surface with its geomorphic development.

The change to fluvial islands over the past five decades represents continued geomorphic evolution of the Lower Mississippi. This is of interest because, although it occurs during a period in which sediment supply has dramatically decreased, with the influence of channel engineering there remains sufficient coarse sediment to drive fluvial landform evolution along the Lower Mississippi.

How to cite: Hudson, P.: Continued evolution of the Lower Mississippi: changes to fluvial islands over five decades (1965 to 2015), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11273, https://doi.org/10.5194/egusphere-egu2020-11273, 2020.

High Arctic erosion processes coupled with physical and chemical mobilisation of abundant soil organic carbon (SOC) stocks may play a critical role in driving Arctic biogeochemical cycles. The role of internal catchment dynamics such as detachment, transport, and colluvial/alluvial storage in controlling the generation, recycling, and export of sediment and SOC is poorly understood. We formulate a sediment and carbon budget for the 8140 km² Alaskan Kuparuk Catchment using a 1985-2017 Landsat NDVI imagery record to delineate bank erosion and Google Earth^TM to map landslide events. We calculate: 1) average inputs of sediment by alluvial bank erosion and landslides (including active layer detachments and thaw slumps), 2) transport fluxes from landslide deposits by spatially modelling fluvial transport capacity, and 3) total outputs from a record of suspended sediment collected at the catchment outlet. We calculate carbon export by estimating carbon erosion using the concentration of SOC as calculated by the Northern Circumpolar Soil Carbon Database. Alluvial bank erosion (0.6 ± 0.12 Tg yr⁻¹) exceeded catchment sediment yield by an order of magnitude (0.06 Tg yr⁻¹), demonstrating that recycling of sediment between floodplains, bars, and channels dominates the sediment budget of this catchment. Landslides are the dominant input of new sediment to the system, contributing 11 Tg of sediment (17 Tg including channel-disconnected). When considering the average export rate from transport-limited landslide deposits, this flux (between 0.008 and 0.4 Tg yr⁻¹) is in near equilibrium with the average annual flux from the catchment (0.06 Tg yr⁻¹). SOC inputs from bank erosion (932 t yr⁻¹) explained the majority of estimated 1505 ± 114 t yr⁻¹ POC outputs. Our work demonstrates that the annual erosion and redeposition of sediment in Arctic permafrost catchments greatly exceeds net export. Current measurements of sediment fluxes in a warming Arctic considerably underestimate total sediment and SOC mobilisation from carbon rich active layers.

How to cite: Matthews, F., Hales, T. C., and Ahmed, J.: A sediment budget approach to quantify sediment fluxes and organic carbon mobilisation in an Arctic catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11359, https://doi.org/10.5194/egusphere-egu2020-11359, 2020.

       In the area of Mt Gongga (Hengduan range, China) most glaciers are experiencing considerable retreat and mass loss since the early 20th century. Drainage of recently deglaciated surfaces delivers fine sediments thus affecting patterns of sediment delivery with impacts on water quality. Research in the area indicates significant differences between sediment at high flows and low flows in the same river during different seasons. High level flows were usually caused by heavy rainfall events or continuous rainfall that erode the slopes by sheet, rill and gully erosion and transport important amounts of sediments to streams leading to significant increases in river sediment flux. During low flows subsurface soil flux during spring and the direct discharge at the outlet of the glacier result in much less sediment load and mean suspended sediment concentration compared with high flows. The runoff volume, hydrograph peak, sediment load and mean suspended sediment concentration in high flows are as much as an order of magnitude higher than in low flows. Therefore, it is of great significance exploring the provenance of fine sediment during high flows and low flows to assess if there are differences in the contributing sources of sediments.

          For this purpose during a 2 weeks field campaign in May 2016 in the frame of IAEA INT5153 project, source sediment samples and channel bed sediment mixtures were collected along the river valley of the Hailuogou Glacier. Three main sources were identified: surface glacier materials, old moraines and recent moraines. Composite surface samples (2 cm) were created of 10 subsamples in each representative site for surface glacier materials. Following the same scheme on old lateral moraines 10 sites were selected from the more mineral blocky deposits to the most vegetated parts at higher altitudes. On recent moraines 12 sites with different stages of vegetation cover were sampled. Starting from the glacier tongue a total of 7 fine sediment mixtures were collected along the river of which 3 composite samples corresponded to the dry season with low flow and 4 samples corresponded to high flow.  A new consensus test method and an unmixing model were used to estimate the apportionments of the sediment sources to the sediment loads. The results showed that the contribution of different sources to the sediment mixture deposits varied along the river showing different provenance for the low and high flow suggesting different mechanisms of sediment generation during melting and dry seasons. This study is of interest for gaining knowledge on changing dynamics of sediment in regions were the rapid disappearance of glaciers and snow as in Mt. Gongga, has increased the mobilization and transport of sediment loads with consequences for the local population.

How to cite: Chen, J., Lizaga, I., Zhang, X., and Navas, A.: The difference of sediment sources between high flows and low flows in the Hailuogou Glacier stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13337, https://doi.org/10.5194/egusphere-egu2020-13337, 2020.

Snow avalanches represent a common phenomenon in Maramureş Mountains (Eastern Carpathians, Romania) where they occur frequently on higher steep slopes and reach in the runout zones the valley bottoms below 1000 m a.s.l. The presence of particular topo-climatic conditions influences the patterns of avalanche activity in terms of past frequency and spatial extent along the slope valleys. As the past snow-avalanche activity is not documented by written reports in the area, reliable information about avalanche history is missing. However, the slopes are forested, trees repeatedly disturbed by snow avalanches record evidence of past events. For this study we reconstructed the avalanche activity using tree rings as a source of proxy data. To date the snow-avalanche history, dendrochronological investigations have been carried out in two avalanche paths, along which living trees showed clear external signs of past disturbances related to mechanical impacts produced by snow avalanches. In each investigated path, a total number of 52 and respectively 118 trees have been sampled and their spatial position recorded with a GPS device. Tree-growth anomalies (e.g. scars, callus tissues, the onset sequences of tangential rows of traumatic resin ducts, compression wood, growth suppression and release sequences) related to snow avalanche disturbance identified within tree rings served to reconstruct past events with an annual resolution. The results indicate that, apart the 2005 major event witnessed and also confirmed by tree-ring dating, multiple other events have been reconstructed since the beginning of 20^th century. Despite some inherent limitations of tree-ring methods in reconstructing past avalanche events, these dendrochronological investigations confirm their utility in deciphering the patterns of avalanche activity in Maramureş Mountains. Tree-ring studies contribute to a better understanding of the role of topographical and climatic factors which influence the spatio-temporal occurrence of snow avalanches.

This study represents a contribution to the joint research project 09-AUF, ‘‘Activité des avalanches de neige dans les Carpates Orientales Roumaines et Ukrainiennes - ACTIVNEIGE’’, co-funded by the Agence Universitaire de la Francophonie (AUF) and Institutul de Fizică Atomică (IFA), Romania.

How to cite: Decaulne, A., Răchită, I.-G., Hotea, M., Chiş, V. T., and Pop, O. T.: Reconstructing snow-avalanche activity with tree rings in Maramureş Mountains (Eastern Carpathians, Romania), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20060, https://doi.org/10.5194/egusphere-egu2020-20060, 2020.

A characteristic feature of the contemporary cliff morphology of the Southern Baltic Baltic are erosional-denudational valleys, which are an important element of the contemporary morphogenetic system. Detailed observations combined with the use of GIS methods were carried out on the Wolin Island. Over a length of about 4 km, several landforms have been distinguished, which are clearly marked in the relief. These forms show the course of NW-SE and are characterized by various morphometric features. Within the studied area, types of valleys with postglacial assumptions as well as fresh erosive cuts were identified. At the turn of the Pleistocene / Holocene, forms of late-glacial genesis were transformed by flushing and erosion processes. Progressive abrasion (cliff top recession rate of 0.22 m / year) has an impact on the further development of the valleys, whose bottoms are currently suspended in relation to the foot of the cliff.

The aim of the study is to present detailed morphometry, lithology of sediments as well as the genesis of separated erosion and denudation valleys.

Based on the research on a selected experimental catchment (recognized as a representative form) located in the edge zone of the cliff, detailed morphological and lithological studies were carried out. In the longitudinal profile of the analyzed valleys, landslides were found in the lower part, which is an effect of an increased dynamics of abrasive processes, while the upper part of the valleys has erosive and denudative character.

Based on the conducted experimental research, it is possible to separate in the longitudinal profile of the valleys the zone of impact of coastal processes from the zone which is shaping by erosion and denudation processes.

Separated erosion and denudation valleys affect both the morphology of the coast and modify the contemporary morphogenetic system of the cliff coast of the Southern Baltic.

How to cite: Paluszkiewicz, R., Kostrzewski, A., and Winowski, M.: Erosional-denudational valleys on the Wolin Island cliff coast (Southern Baltic) and their impact on the morphological development of the coast, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20454, https://doi.org/10.5194/egusphere-egu2020-20454, 2020.

We investigate the interplay between riverine islands dynamics in a large tropical wandering river and their use by local communities for agricultural production. The study focuses on a piedmont reach of the Huallaga river, which drains the Peruvian Amazon. Riverine islands are characterized by a high space-time variability in active wandering river systems like the Huallaga, which results from biophysical interactions among flow, sediment transport and riparian vegetation. Despite the rapid rates of planform changes, islands in the Huallaga are extensively used by local farmers who mainly rely on rainfed, low tech agriculture. Thanks to the high nutrient availability in their soil, dynamic riverine islands are offering a natural solution to the advancing degradation of soils due to the progressive increase of intensive monoculture in nearby floodplain areas. The possibility of using intact fields, rich in organic matter, pushes the local populations to colonize riverine islands, challenging their dynamism and high erosion. Through a combination of participatory surveys, field measurements and remote sensing analysis of the recent (30 years) reach-scale island dynamics we investigate whether the benefits of cropping in a riverine island are more relevant than the damages related to their intense morpho-dynamics. Challenges to such biophysical-social system are posed by planned and ongoing infrastructural development in the catchment, affecting the flow and sediment supply regimes.

How to cite: Serrao, L., Balcázar Terrones, L. E., Huamaní Yupanqui, H. A., Rengifo Trigozo, J. P., and Zolezzi, G.: Agricultural colonization of dynamic riverine islands in a tropical wandering river, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20579, https://doi.org/10.5194/egusphere-egu2020-20579, 2020.

Mediterranean regions have always been affected by wildfires. However, no studies investigating post-fire hydrological responses and erosion at the watershed scale (~>10 km2) were conducted in Mediterranean. In this study, the discharge and sediment measurements at the outlet of a Mediterranean watershed were observed to test changes in hydrological responses and sediment loads before and after the fire. Besides, aid by the PCA analysis and analysis of connectivity patterns and changes using the index of connectivity (IC), we analyze the hydrological responses and erosion to a wildfire at the watershed scale. Although most of vegetation was removed after the wildfire, it did not, overall, lead to a significant increase in hydrological responses and sediment loads at the watershed scale. Our results can be explained by three major factors. Firstly, much lower rainfall the first two hydrological years after the fire occurred in our watershed. Secondly, as a result of the scale dependency of hydrological and erosion processes, fire-enhanced overland flow and sediment transport occurred locally on hillslope with high burn severity but did not (yet) reach the outlet. Finally, and arguably, most importantly, connectivity in our study area is relatively low and, although it increases after the fire, it remains generally low. Even though post-wildfire connectivity in our watershed increased by 20%, this increase in connectivity was mainly located in the upstream-most part of this catchment, with much less increased connectivity in the downstream areas, which are closer to the catchment outlet. We concluded that the fire consumed vegetation and altered hydrology and erosion processes but didn’t significantly influence downstream water quantity and quality. Connectivity linked to burn severity was suitable for evaluating the effect of wildfire on hydrological responses and erosion. Moreover, this method also appears to be reasonable in assessing and mitigating post-fire water contamination risk.

How to cite: Wu, J., Baartman, J. E. M., and Nunes, J. P.: Low watershed hydrological and erosion response after fire can be explained by connectivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20784, https://doi.org/10.5194/egusphere-egu2020-20784, 2020.